JP4057250B2 - Organic EL element and organic EL display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic EL element (organic electroluminescence element). More specifically, the present invention relates to a blue organic EL element having high luminous efficiency, high luminance, and long life and an organic EL display using the same.
[0002]
[Prior art]
The organic EL element is promising as a self-luminous flat display element. Unlike an inorganic EL element, the organic EL element is driven by alternating current and does not have a restriction that it is necessary to apply a high voltage, and it is considered that multicolorization is easy due to the diversity of organic compounds. For this reason, it is expected to be applied to color displays and the like, and research is actively conducted.
[0003]
When an organic EL element is applied to a color display, it is necessary to obtain light emission of three colors of red, green, and blue which are three primary colors. Of these, many examples of green light emission have been reported. For example, green elements include elements using tris (8-quinolinol) aluminum (Applied Physics Letters 51, P913 (1987)), elements using diarylamine derivatives. (Japanese Patent Laid-Open No. 8-53397) is known.
[0004]
Regarding organic EL elements that can emit red light, for example, Japanese Patent No. 2795932 provides an organic EL element in which blue light emission is wavelength-converted in a fluorescent dye layer, and Japanese Patent Application Laid-Open No. 7-272854. Kaihei 7-288184, JP-A-8-286033, etc. describe inventions of red light emitting organic EL elements in which a light emitting layer capable of emitting green or blue light is doped with a red fluorescent dye.
[0005]
As for the blue light emitting element, an element using a stilbene compound (Japanese Patent Laid-Open No. 5-295359), an element using a triarylamine derivative (Japanese Patent Laid-Open No. 7-53955), an element using a tetraaryldiamine derivative (Japanese Patent Laid-Open No. No. 8-48656) and devices using a styrylated biphenyl compound (Japanese Patent Laid-Open No. 6-132080) are known.
[0006]
The organic EL element is a carrier injection type element that emits light by injecting hole carriers from the anode and electron carriers from the cathode, and recombining these carriers, unlike the inorganic EL element of electric field excitation type light emission. In order to improve the performance of such an organic EL element, a laminated element in which a light-emitting layer and a charge transport layer are combined is more desirable than a single-layer element composed only of a light-emitting layer. This is because, in a laminated element, an appropriate combination of a light emitting material and a charge transport material reduces an energy barrier when injecting holes from the anode or electrons from the cathode, facilitating injection of charges, The charge transport layer functions as a blocking layer that suppresses passage of holes or electrons from the light emitting layer. As a result, the numerical balance between holes and electrons in the light-emitting layer is improved, and as a result, recombination is effectively performed and EL light emission efficiency is considered to be improved. Therefore, in order to produce a highly efficient organic EL element, improvement of the blocking property of holes and electrons at the interface between the light emitting layer and the charge transport layer becomes an issue.
[0007]
Conventionally, in the case of a red or green light emitting layer that also has hole transportability, since the energy gap of the light emitting material is relatively small, there are many electron transport materials having a larger ionization potential than the light emitting material. However, unlike red and green light-emitting materials, blue light-emitting materials have a large energy gap (energy difference between HOMO-LUMO levels), and are usually tris (8-quinolinol) aluminum, bis. (8-Quinolinol) The ionization potential is larger than the electron transport layer such as 8-hydroxyquinoline metal complexes such as magnesium and oxadiazole derivatives. As shown in FIG. 5, for example, tris (8-quinolinol) aluminum (Alq), which is generally widely used as an electron transport material or a green light emitting material, for example._Three) Has an ionization potential of 5.67 and good carrier transportability and film formability, but 4,4′-bis (2,2′-diphenylvinyl) biphenyl, which is an example of a hole transporting blue light-emitting material. Since the value is smaller than the ionization potential 5.9 of (DPVBi), the hole blocking property is small for the hole transporting blue light emitting material. For this reason, holes pass through, and thus there are disadvantages such as a decrease in EL emission efficiency based on a decrease in hole-electron recombination efficiency, a decrease in maximum luminance, and a change in emission site.
[0008]
[Problems to be solved by the invention]
The present invention aims to ameliorate the problems of the above blue organic EL elements. I. In the E chromaticity diagram (1931), blue elements in the BLUE, GREENISH BLUE, and PURPLISH BLUE regions whose X and Y coordinates are (0.25, 0.25) or less are improved in brightness, efficiency, and lifespan. For the purpose.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides organic EL elements and organic EL displays shown in the following [1] to [8].
[0010]
[1] An organic EL device having a light emitting layer made of an organic compound thin film and an electron transporting layer between different electrodes, and the light emitting layer emits blue light, wherein the electron transporting layer has the following general formula (1) The organic EL element characterized by containing the compound represented by these.
[Chemical 9]
(M in the general formula (1) represents a metal atom. R¹~ R⁶Each independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted cyclooxy group. Represents an alkyl group or a cyano group, R¹~ R⁶At least one of them is a substituted or unsubstituted aryl group, and R¹~ R⁶May be the same or different. L is a coordination having a halogen atom, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted cycloalkyl group Represents a child. n represents 1 or 2, and when n is 2, R¹~ R⁶The groups represented by the same symbols may be the same or different. )
[0011]
[2] R in the compound represented by the general formula (1)^FourIs an aryl group. The organic EL device of [1], wherein
[0012]
[3] The organic EL device of [2], wherein the compound represented by the general formula (1) is a compound of the following formula (1a).
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[0013]
[4] The organic EL device of [2], wherein the compound represented by the general formula (1) is a compound of the following formula (1b).
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[0014]
[5] The organic EL device according to [1] to [4], wherein the electron transport layer contains a plurality of compounds represented by the general formula (1).
[0015]
[6] The organic EL device according to [5], wherein the electron transport layer contains the compound of the formula (1a) and the compound of the formula (1b).
[0016]
[7] The light emitting layer contains a compound represented by the following general formula (2) or the following general formula (3) and a compound represented by the following general formula (4) [1] Organic EL element of [6].
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(Where R₁~ R_FourEach independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an amino group, or a cyano group, and when n is plural,₁~ R_FourThe groups having the same symbol represented by the above may be the same or different, and R_FiveAnd R₆Each independently represents an aryl group having 6 to 12 carbon atoms which may have a substituent, and n represents an integer of 3 to 6. )
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(Wherein M represents a metal atom, R¹¹~ R¹⁹Each independently represents one selected from a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, and an aryloxy group, which may be the same or different, and R¹¹~ R¹⁴, R¹⁵~ R¹⁹May combine with each other to form a saturated or unsaturated ring, R^aIs R¹¹~ R¹⁹A group which may have the same substituent as R^bIs a heteroatom and R^aAnd R^bMay independently or combine with each other to form a heterocycle, n represents 2 or 3, and R represents a divalent group. )
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(Where R_{twenty one}~ R_{twenty four}Each independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an amino group, an alicyclic ring, or a heterocyclic ring;_{twenty one}~ R_{twenty four}The groups having the same symbol represented by the above may be the same or different, and R_{twenty five}And R₂₆Each independently represents an aryl group which may have a substituent, and n represents a positive integer. )
[0017]
[8] An organic EL display comprising the organic EL elements of [1] to [7].
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The compound of the general formula (1) used for the electron transport layer in the present invention, for example, a metal complex using gallium as the central metal and an 8-hydroxyquinoline derivative as the ligand, has an ionization potential larger than that of the blue light-emitting layer as shown in FIG. Therefore, the hole blocking property is large, and the confinement effect of carriers in the light emitting layer and the recombination probability are increased. Therefore, a blue element with high efficiency and high luminance can be obtained. Further, since the driving conditions are relaxed, the life can be extended. Furthermore, this material has very good film formability, excellent thermal stability, and improves the heat resistance temperature of the device.
[0019]
By using the material and organic EL element structure used in the organic EL element according to the present invention, holes injected from the anode are reliably blocked in the electron transport layer, and electrons injected from the cathode emit light. Blocking with a layer improves carrier recombination efficiency. For this reason, the organic EL device according to the present invention has no reduction in luminous efficiency even in the blue light-emitting device, and the maximum luminance of the organic EL device according to the present invention is the same as that of the conventional Alq._ThreeCompared to the case of the organic EL element using the above, it can be made larger.
[0020]
Further, in the organic EL device according to the present invention, holes do not pass through and the power efficiency is much better than that of the conventional device, so that low power consumption is possible. Furthermore, in the organic EL device according to the present invention, Since the device can be driven under a low load condition, the lifetime of the element is also extended. Furthermore, by using an electron transport layer having a high ionization potential, a blue light emitting layer having a high ionization potential can be used, and accordingly, the energy gap of the blue light emitting layer can be increased accordingly. Therefore, in the organic EL device according to the present invention, the emission wavelength can be shortened. As a result, it is possible to produce an organic EL element with good blue chromaticity, which has been difficult with conventional materials, and to use various organic chromaticity elements in combination with other conventional organic EL elements. Can be generated.
[0021]
The organic EL device according to the present invention has a light emitting layer made of an organic compound thin film and an electron transport layer between a cathode and an anode and between different electrodes, and examples thereof include the following three combinations. It is done.
(1) Anode, light emitting layer, electron transport layer, cathode (see FIG. 1)
(2) Anode, hole transport layer, light emitting layer, electron transport layer, cathode (see FIG. 2)
(3) Anode, hole injection layer, hole transport layer, light emitting layer, electron transport layer, cathode (see FIG. 3)
The hole transport layer and the hole injection layer are both intermediate layers made of an organic thin film provided between the anode and the light emitting layer in order to facilitate the movement of holes from the anode to the light emitting layer. Is a hole transport layer and the smaller ionization potential is referred to as a hole injection layer.
[0022]
The anode used in the organic EL device according to the present invention injects holes into a hole transport layer (a hole injection layer when a hole injection layer is provided, or a light emitting layer when a hole transport layer is not provided). It is effective to have an ionization potential and work function of 4.5 eV or more. Specific examples of the anode material used in the present invention include indium tin oxide alloy (ITO), tin oxide (NESA), gold, silver, platinum, copper and the like.
[0023]
The hole injection material for forming the hole injection layer of the organic EL device according to the present invention is not particularly limited, and examples thereof include metal phthalocyanine or metal-free phthalocyanine represented by the structural formula (5) below. .
[0024]
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(In the above formula, X is hydrogen, M is Cu, VO, TiO, Mg, H₂It is at least one selected from more. )
[0025]
Furthermore, arylamine compounds represented by the following structural formulas (6) to (9):
[0026]
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[0027]
And N, N′-diphenyl-N, N′-bis (α-naphthyl) -1,1′-biphenyl-4,4′-diamine (abbreviated as α-NPD).
[0028]
Moreover, the hole transport material for forming the hole transport layer used for the organic EL element of this invention is not specifically limited. As such a material, any compound can be used as long as it is a compound usually used as a hole transport material. As such a hole transport material, for example, a diamine compound represented by the following structural formula (10),
[0029]
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[0030]
Bis (di (p-tolyl) aminophenyl) -1,1-cyclohexane, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4, 4 '-Diamine, N, N'-diphenyl-N, N'-bis (α-naphthyl)-(1,1'-biphenyl) -4,4'-diamine, and the like, and triamine compounds, tetraamines And similar compounds and starburst type molecules.
[0031]
In addition, as the cathode of the organic EL device according to the present invention, a material having a work function smaller than that of the anode can be preferably selected in order to effectively inject electrons into the electron transport layer. Although it does not specifically limit as such a cathode material, Specifically, elements, such as an indium, aluminum, and magnesium, magnesium-indium, magnesium-aluminum, aluminum-lithium, magnesium-silver etc. alloy, or the said element and said alloy And mixed metals or alloys can be used.
[0032]
Materials used for electron transport layer or electron injection layer
The electron transport layer or the electron injection layer of the organic EL device according to the present invention contains at least one compound represented by the general formula (1). There is no clear difference between the electron transport layer and the electron injection layer, and both are intermediate layers provided between the cathode and the light emitting layer to facilitate the movement of electrons to the light emitting layer. In a two-layer structure, the ionization potential with the larger ionization potential is sometimes referred to as the electron injection layer, and the smaller with the electron transport layer as the electron transport layer. It is as a layer.
[0033]
Examples of the compound represented by the general formula (1) include R¹~ R⁶Wherein at least one of them is a substituted or unsubstituted aryl group, in particular R^FourIs preferably an aryl group. R¹~ R⁶Having at least one substituted or unsubstituted aryl group improves the heat resistance of the electron transport material, i.e., increases Tg, makes it difficult for crystallization to occur in a high temperature environment, and Good film formability.
[0034]
As an example of the compound represented by the above general formula (1), specifically, the compound bis (2-methyl-5-phenyl-8-quinolinol) (1-phenolate) gallium of the above formula (1a) And the compound bis (2-methyl-5-phenyl-8-quinolinol) chlorogallium of the formula (1b). Moreover, it is preferable that an electron carrying layer contains multiple types of compounds represented by General formula (1), especially the compound of Formula (1a) and the compound of Formula (1b). As specific heat resistance and film formability data, the compound of formula (1a) has a surface roughness R of a single layer film at Tg: 118 ° C. at room temperature._Z: 2.56 nm, surface roughness R after processing the same monolayer film at 85 ° C. for 10 minutes_Z: Surface roughness R of monolayer film at room temperature with 3.31 nm, compound of formula (1a) and compound of formula (1b) 9: 1_Z: Surface roughness R after processing the same monolayer film at 85 ° C. for 10 minutes: 1.97 nm_Z: 2.05 nm. In contrast, the 5-position (R) of the compound of formula (1a)^FourBis- (2-methyl-8-quinolinol) (1-phenolate) gallium having no phenyl group is equivalent to the surface roughness R of the monolayer film at Tg: 89 ° C. at room temperature._Z: Surface roughness R after treating the same monolayer film at 3.96 nm at 85 ° C. for 10 minutes_Z: 18.97 nm. From these, when an aryl group is introduced as a substituent in the compound of formula (1), Tg is improved, and unevenness due to crystallization of the surface is suppressed in a high-temperature atmosphere, and in particular, when a plurality of compounds are used, suppression of crystallization is suppressed. It is suggested that it is remarkable. When an aryl group is introduced, the ionization potential tends to decrease, but R^FourIn the case of having an aryl group, the heat resistance is improved, the increase in ionization potential is small, and the property balance is good. The ionization potential of the compound of formula (1a) is 6.00, and the ionization potential of the compound of formula (1b) is 5.93.
[0035]
The electron transport layer or the electron injection layer of the organic EL device according to the present invention is formed of a single layer, a mixed layer, or a multilayer by using the materials described above alone or in combination of two or more. When the electron transport layer of the organic EL device according to the present invention has a two-layer structure, the one having a higher ionization potential is generally referred to as an electron injection layer (a smaller one is referred to as an electron transport layer). . In the present invention, among materials used for the electron transport layer described above, it is preferable to select a material having a Tg measured by DSC (Differential Scanning Calorimetry) exceeding 80 ° C., more preferably , Tg is preferably 85 ° C. or higher.
[0036]
Furthermore, when a plurality of types of organometallic complexes represented by the general formula (1) are contained in the electron injection layer or the electron transport layer, the luminance can be kept high. That is, when only one kind of the above organometallic complex is used in the electron injection layer or the electron transport layer, the aggregation and crystallization of the thin film progresses when used at a high temperature for a long time, and the electron injection property or the electron transport property is deteriorated. Tend. On the other hand, when two or more of the above organometallic complexes are contained, the amorphousness (amorphous property) becomes high, so that aggregation and crystallization hardly occur even when used for a long time. Therefore, electron injection characteristics or electron transport characteristics Can be suppressed. When a plurality of types of electron transport materials are contained, although the decrease in electron transport characteristics can be reduced as compared with the case of a single substance, the initial characteristics are decreased. % Is preferable, and if it is larger than 99%, the effect of suppressing the decrease in electron transport properties is small, which is not preferable.
[0037]
Materials used for light emitting layer
The material used for the light emitting layer of the organic EL device of the present invention is not particularly limited except that the ionization potential is smaller than that of the electron transport layer, and any compound that is usually used as a blue light emitting material can be used. It is desirable to contain one or more compounds selected from the formulas (2) to (3). However, when a hole transport layer is used in combination, one having a higher ionization potential than the hole transport layer is used.
[0038]
More specifically, examples of the compound of the formula (2) include compounds shown in Table 1 below.
[0039]
[Table 1]
[0040]
More specifically, examples of the compound of the formula (3) include compounds of the following formulas (3-1) to (3-3).
[0041]
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[0042]
In formulas (3-1) to (3-3), M and R¹¹~ R¹⁹And n have the same meaning as in formula (3). Examples of such a benzoxazole compound represented by the formula (3-1), an oxadiazol compound represented by the formula (3-2), and an imidazole compound represented by the formula (3-3) include: Compounds as shown in Table 2 below are mentioned. Unless otherwise indicated, the compound represented by this Table 2 contains all the compounds represented by Formula (3-1)-(3-3). That is, for example, in Table 2, Compound No. In the compound of 301, the compound corresponding to the formula (3-1) is a compound of the formula (17) described later, and the compound corresponding to the formula (3-2) is Zn (IMZ).₂Thus, the compound corresponding to the formula (3-3) becomes a compound of the formula (18) described later.
[0043]
[Table 2]
[0044]
Moreover, you may dope by using the said compound as a host, the amino substituted distyryl arylene derivative shown by following formula (11)-(13), a perylene derivative, etc. as a guest.
[0045]
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[0046]
Examples of the compounds represented by the general formulas (2) and (3) include Japanese Patent Publication No. 7-119407, Japanese Patent Application Laid-Open No. 3-231970, Japanese Patent Application Laid-Open No. 8-199162, Japanese Patent Application Laid-Open No. 8-333569, Examples thereof include compounds disclosed in JP-A-8-333283. Examples of such compounds are:
[0047]
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[0048]
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[0049]
Furthermore, tris [(2-phenyl-5-m-phenoxy) -1,3,4-oxadiazole] aluminum (Al (OXD)_Three) (One of compound No. 305 in Table 2 represented by formula (3-2)) and the like.
[0050]
In the present invention, the compound represented by the general formula (2) or (3) may be doped as a host and the compound represented by the general formula (4) as a guest. As a result, the light emission performance is further improved, and aggregation is less likely to occur due to doping, thereby improving the heat resistance and the light emission lifetime. In particular, the case where the compound represented by the general formula (2) is a host and the compound represented by the general formula (4) is a guest is preferable. In this case, in the compound represented by the general formula (4), R_{twenty one}~ R_{twenty four}Is a hydrogen atom, R_{twenty five}And R₂₆Is more preferably a phenyl group, and n is 1 to 6, particularly 3. The above effect can be obtained because the chemical structures of the host material and guest material are similar.
[0051]
Next, a method for forming an organic EL element according to the present invention will be described. The formation method of each layer of the organic EL element according to the present invention is not particularly limited. The organic thin film layer used in the organic EL device of the present invention can be formed by a known method. Examples of such a method include a vacuum deposition method, a molecular beam deposition method, and a coating method. As the coating method, for example, it can be formed by a dipping method, a spin coating method, a casting method or the like using a solution or a dispersion. By forming each layer as shown in the above configuration by such a method, the organic EL element according to the present invention can be formed.
[0052]
The film thickness of each organic layer of the organic EL device according to the present invention is not particularly limited. In general, however, if the film thickness is too thin, defects such as pinholes are likely to occur. Necessary and inefficient. For this reason, it is preferable to form the film thickness of each organic layer in the range of, for example, several nm to 1 μm.
[0053]
The electron transport material represented by the general formula (1) of the present invention is a known method using, for example, a gallium compound and a compound having a ligand residue of the formula (1) represented by the following formula (19) as raw materials. Can be synthesized. In addition, as M in the other formula (1), a trivalent metal having higher ionization energy than aluminum can be applied.
[0054]
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[0055]
Examples of the gallium compounds include, but are not limited to, ionic gallium compounds such as alkyl gallium, gallium alkoxide, gallium halide, gallium nitride, and gallium oxide. Further, the ligand of the general formula (19) can have a 2-coordinate quinoline residue such as 8-hydroxyquinoline, 2-methyl-8-hydroxyquinoline, and the L ligand includes fluorine, Residues containing halogens such as chlorine, bromine and iodine, alkoxy groups which may have a substituent, aryloxy groups which may have a substituent, and alkyl groups which may have a substituent Etc., and these can have one coordination. Such a complex of the general formula (1) used in the present invention, the ligand of the general formula (19) and the ligand of the L are polar organic solvents, for example, alcohols such as methanol and ethanol. It can be obtained by reacting in an ionic solvent such as a solvent, or a nonpolar solvent such as an aromatic solvent such as benzene or toluene, or an alicyclic solvent such as tetrahydrofuran.
[0056]
Moreover, the luminescent material represented by General formula (2) used for this invention is compoundable by a well-known method. A method of deprotonating a phosphonic acid ester having a phenyl group by allowing a base to act in the presence of a solvent as described above, followed by alkenylation (for example, Wittig reaction) by adding a carbonyl compound such as benzophenone, or adding a phosphonic acid ester to a base And deprotonating, and then reacting with a dialdehyde compound having a phenyl group to alkene (the same reaction as described above, for example, Wittig reaction). As the above-mentioned base, alkyl alkali metal salts such as alkyl lithium, alkali metal hydrides such as lithium aluminum hydride and sodium hydride, sodium amide, caustic soda and the like can be used.
[0057]
Moreover, the luminescent material represented by the general formula (3) used in the present invention can be synthesized by a known method. For example, benzoic acid chloride and benzoic hydrazide are reacted in the presence of dioxane to form diacyl hydrazide, dehydrated to form an oxadiazole skeleton, and then the protective group is eliminated. Next, the compound having an oxadiazole residue obtained by removing the protecting group and a zinc compound, for example, zinc acetate, in the presence of a polar solvent such as alcohol such as methanol, ethanol, isopropyl alcohol, or n-hexane Reaction in the presence of a nonpolar solvent such as oxadiazole zinc complex.
[0058]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to a following example and is not interpreted.
[0059]
Ionization potential
The ionization potential of each material was measured by depositing each material to be obtained on a glass substrate and using AC-1 manufactured by Riken Keiki Co., Ltd. under atmospheric pressure and 24 ° C. and relative humidity of 40%. In addition, the film formation used the method similar to the film formation mentioned later.
[0060]
Tg (glass transition temperature)
The material used for the electron transport layer was measured using DSC-50 manufactured by Shimadzu Corporation.
[0061]
Example 1
FIG. 3 shows a cross-sectional structure of the organic EL element according to Example 1. The organic EL element according to this example includes a glass substrate 1, an anode 2 and a cathode 3 formed on the glass substrate 1, a hole injection layer 4 sandwiched between the anode 2 and the cathode 3, a positive electrode It consists of a hole transport layer 5, a light emitting layer 6, and an electron transport layer 7.
[0062]
Hereinafter, a manufacturing procedure of the organic EL element according to Example 1 will be described. First, ITO (indium tin oxide) was formed on a glass substrate by sputtering so as to have a film thickness of 1300 mm (130 nm), and the anode 2 was obtained. The sheet resistance at this time was 12Ω / □. The prepared ITO glass substrate was subjected to ultrasonic cleaning with pure water and isopropyl alcohol, and then dried on boiling isopropyl alcohol. Furthermore, after this substrate was cleaned by a UV ozone cleaning device, it was attached to a substrate holder of a vacuum deposition device.
[0063]
Next, 100 mg of 4-phenyl-4 ′, 4 ″ -bis [di (3-methylphenyl) amino] triphenylamine as a hole injection layer and α-NPD as a hole transport layer in a molybdenum boat. 100 mg, 9,10-bis [4- (2,2-diphenylvinyl) phenyl] anthracene as the light emitting layer, and bis (2-methyl-5-phenyl-8-quinolinol) (1-phenolate) as the electron transport layer ) 100 mg of gallium was added and attached to different energizing terminals. Bis (2-methyl-5-phenyl-8-quinolinol) (1-phenolate) gallium has an ionization potential of 6.00 eV and Tg of 118 ° C.
[0064]
1 × 10 in the vacuum layer^-FourAfter exhausting to Pa, the boat containing 4-phenyl-4 ′, 4 ″ -bis [di (3-methylphenyl) amino] triphenylamine was energized, and the film thickness was 0.3 nm / Sec. Film formation was performed until the thickness reached 35 nm. Next, the boat containing α-NPD was energized to form a film at a deposition rate of 0.3 nm / Sec until the film thickness reached 15 nm. Next, the boat containing 9,10-bis [4- (2,2-diphenylvinyl) phenyl] anthracene was energized to form a film at a deposition rate of 0.3 nm / Sec until a film thickness of 45 nm was reached. Next, a boat containing bis (2-methyl-5-phenyl-8-quinolinol) (1-phenolate) gallium was energized to form a film at a deposition rate of 0.3 nm until a film thickness of 35 nm was reached.
[0065]
A stainless-steel shadow mask was attached to the top of the device thus fabricated. Here, 3 g of aluminum was put into a BN boat and attached to a terminal for energization. Similarly, 500 mg of Li was placed in a tungsten filament and attached to another energizing terminal. Vacuum layer 1x10^-FourAfter evacuating to Pa, energization was performed so that the deposition rate of aluminum was 0.4 nm / Sec, and at the same time, energization was performed using another deposition power source so that the deposition rate of lithium was 0.02 to 0.03 nm / Sec. . When the vapor deposition rates of both materials have stabilized, the shutter is opened, and when the mixed film thickness reaches 30 nm, the lithium evaporation power supply is turned off, and further, the aluminum film is formed until the aluminum film has a thickness of 170 nm. 3 was formed to produce an organic EL element.
[0066]
When a DC voltage of 17 V was applied between the anode and the cathode of the obtained organic EL element, 38500 cd / m², CIE chromaticity coordinates (0.15, 0.14) @ 1000 cd / m²4.8lm/W@200cd/m²Of blue light emission was obtained. The above value is luminance 1000 cd / m²CIE chromaticity coordinates (X, Y) and luminance at 200 cd / m²Means the luminous efficiency Z (lm / W). The driving test of this element was conducted at an initial luminance of 100 cd / m in nitrogen.²As a result, the luminance half time was 20000 hours or more. Moreover, after storing this element in nitrogen for 20000 hours, as a result of observing a non-light-emitting portion called a dark spot, what was 5 μm immediately after film formation was not significantly changed to 5-7 μm after storage, Growth was not observed. Furthermore, the initial luminance is 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of the driving test, the luminance half time was 510 hours.
[0067]
Comparative Example 1
1,4-bis [4- (2,2-diphenylvinyl) naphthyl] benzene as a light emitting layer is 45 nm, and 2- (4-biphenylyl) -5- (4-t-butylphenyl) -1, as an electron transport layer An organic EL device was produced in the same manner as in Example 1 except that 35-nm of 3,4-oxadiazole was formed by vacuum deposition.
[0068]
When a DC voltage of 17 V was applied between the anode and cathode of this organic EL element, 13700 cd / m²Of blue light emission was obtained. Compared to Example 1, there was no significant difference in CIE chromaticity coordinates, but there was a difference in terms of maximum luminance, efficiency, and lifetime. Furthermore, the initial luminance is 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of the driving test, the luminance half time was 80 hours.
[0069]
Comparative Example 2
An organic EL device was produced in the same manner as in Example 1 except that bis (2-methyl-8-quinolinol) (1-phenolate) gallium was used as the electron transport layer. This organic EL device has an initial luminance of 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of the drive test, the luminance half time was 180 hours.
[0070]
Example 2
A cross-sectional structure of an organic EL device according to Example 2 is shown in FIG. The organic EL element according to this example includes a glass substrate 1, an anode 2 and a cathode 3 formed on the glass substrate 1, a hole injection layer 4 sandwiched between the anode 2 and the cathode 3, a positive electrode It consists of a hole transport layer 5, a light emitting layer 6 made of a host and a dopant, and an electron transport layer 7.
[0071]
An ITO glass substrate prepared in the same manner as in Example 1 was mounted on a vapor deposition machine, and five crucibles made of high-purity graphite were prepared, and 4-phenyl-4 ′ and 4 ′ were separately used as hole injection layers. 1 g of '-bis [di (3-methylphenyl) amino] triphenylamine, N, N'-diphenyl-N, N'-bis (α-naphthyl) -1,1'-biphenyl- as a hole transport layer 1 g of 4,4′-diamine (α-NPD), 1 g of 9,10-bis [4- (2,2-diphenylvinyl) phenyl] anthracene as the luminescent host material, and 4,4′-bis [ 0.5 g of 2- {4- (N, N-di (4-methylphenyl) amino) phenyl} vinyl] biphenyl and bis (2-methyl-5-phenyl-8-quinolinol) (1- Fenora 1 g of a mixture (weight ratio 9: 1) of gallium and bis (2-methyl-5-phenyl-8-quinolinol) chlorogallium was added to each of the terminals for energization.
[0072]
8 × 10 in the vacuum layer^-FiveAfter exhausting to Pa, a hole injection layer and a hole transport layer were formed in the same film thickness as in Example 1 in the same manner as in Example 1. Next, the host 9,10-bis [4- (2,2-diphenylvinyl) phenyl] anthracene and the guest 4,4′-bis [2- {4- (N, N-di (4-methyl)] [Phenyl) amino) phenyl} vinyl] biphenyl is energized, and the current is controlled so that the host becomes 0.3 nm / Sec and the guest becomes 0.02 to 0.03 nm / Sec, and both are stable. At the same time, vapor deposition was started at the same time, and the film was formed until the film thickness reached 45 nm. Next, an electric current was passed through a crucible containing a mixture of bis (2-methyl-5-phenyl-8-quinolinol) (1-phenolate) gallium and bis (2-methyl-5-phenyl-8-quinolinol) chlorogallium. The film was formed at a deposition rate of 0.3 nm until the film thickness reached 35 nm. A cathode was further formed on the device thus prepared in the same manner as in Example 1 to prepare an organic EL device.
[0073]
When a DC voltage of 17 V was applied between the anode and the cathode of the obtained organic EL element, 41500 cd / m², CIE chromaticity coordinates (0.16, 0.17) @ 1000 cd / m²5.6 lm / W @ 200 cd / m²Of blue light emission was obtained. The above value is luminance 1000 cd / m²CIE chromaticity coordinates (X, Y) and luminance at 200 cd / m²Means the luminous efficiency Z (lm / W). The driving test of this element was conducted at an initial luminance of 100 cd / m in nitrogen.²As a result, the luminance half time was 20000 hours or more. In addition, after storing this device in nitrogen for 20000 hours, a non-light emitting portion called a dark spot was observed. As a result, what was 4 to 5 μm immediately after the film formation was 5 to 7 μm after storage. There was no growth. Furthermore, the initial luminance is 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of performing a driving test with, the luminance half time was 850 hours.
[0074]
Example 3
In Example 2, the light emitting guest material 4,4′-bis [2- {4- (N, N-di (4-methylphenyl) amino) phenyl} vinyl] biphenyl was used except that it was not used. Operation similar to 2 was performed and the organic EL element was produced.
[0075]
When a DC voltage of 17 V was applied between the anode and the cathode of the obtained organic EL element, 39500 cd / m², CIE chromaticity coordinates (0.14, 0.14) @ 1000 cd / m²4.91m/W@200cd/m²Of blue light emission was obtained. The above value is luminance 1000 cd / m²CIE chromaticity coordinates (X, Y) and luminance at 200 cd / m²Means the luminous efficiency Z (lm / W). The driving test of this element was conducted at an initial luminance of 100 cd / m in nitrogen.²As a result, the luminance half time was 20000 hours or more. In addition, after storing this device in nitrogen for 20000 hours, a non-light emitting portion called a dark spot was observed. As a result, what was 4 to 5 μm immediately after the film formation was 5 to 7 μm after storage. There was no growth. Furthermore, the initial luminance is 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of the drive test, the luminance half time was 640 hours.
[0076]
Comparative Example 3
Example 2 except that 4,4′-bis (2,2-diphenylvinyl) biphenyl was formed as a light emitting layer host at 45 nm and tris (8-quinolinol) aluminum was formed as an electron transport layer 5 by vacuum deposition at 35 nm. The same operation was performed to produce an organic EL device.
[0077]
When a DC voltage of 17 V was applied between the anode and cathode of this organic EL element, 17000 cd / m²Of blue light emission was obtained. Compared with Example 2, the CIE chromaticity coordinates were not significantly different, but were different in terms of maximum luminance, efficiency, and lifetime. Furthermore, the initial luminance is 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of the driving test, the luminance half time was 210 hours.
[0078]
Comparative Example 4
An organic EL device was produced in the same manner as in Example 2 except that bis (2-methyl-8-quinolinol) (1-phenolate) gallium was used alone as the electron transport layer. This organic EL device has an initial luminance of 200 cd / m in an environment of 85 ° C. in nitrogen.²As a result of the drive test, the luminance half time was 270 hours.
[0079]
Regarding the organic EL elements of Examples 1 to 3 and Comparative Examples 1 to 4 described above, (1) luminance when a DC voltage of 17 V is applied between the anode and the cathode (luminance by applying 17 V), and (2) driving of the element Test in nitrogen with initial brightness of 100 cd / m²Brightness half-time (when the initial brightness is 100 cd / m²(3) Luminance half-life at room temperature), (3) Element drive test under nitrogen at 85 ° C. in an initial luminance of 200 cd / m²Brightness half-time (initial brightness 200 cd / m²Table 3 shows the data of luminance half-life at 85 ° C.
[0080]
[Table 3]
[0081]
(1) Luminance by applying 17V is 30000 cd / m²2) Initial luminance 100 cd / m²Luminance half-time at: room temperature is 20000 hours or longer, (3) initial luminance is 200 cd / m²Luminance half time at: 85 ° C., 500 hours or more can be used as a criterion for determining good characteristics. In Comparative Example 3, the difference in the electron transport layer is compared with Example 2, but the host material of the light emitting layer is also different. The difference in the light emitting layer host material has little influence on the characteristics, and even when the same host material as in Example 2 is used, it is understood that the difference in the electron transport layer greatly affects the characteristics.
[0082]
【The invention's effect】
The organic EL element according to the present invention is a carrier injection type element that emits light by injecting hole carriers from the anode, electron carriers from the cathode, and recombination of these carriers, unlike the electroluminescent inorganic EL element. Yes, because it has a stacked element type structure that combines a light-emitting layer and a charge transport layer, by using an appropriate combination of a light-emitting material and a charge transport material, hole injection from the anode or electron injection from the cathode can be achieved. The energy barrier at the time is reduced, charge injection is facilitated, and the charge transport layer functions as a blocking layer that suppresses passage of holes or electrons from the light emitting layer. This improves the numerical balance between holes and electrons in the light emitting layer. As a result, the recombination of holes and electrons is effectively performed, and the EL luminous efficiency can be improved.
[0083]
By using the specific material and element structure used in the organic EL element according to the present invention as described above, holes injected from the anode are reliably blocked in the electron transport layer and electrons injected from the cathode are used. Is blocked by the light emitting layer, thereby improving the carrier recombination efficiency. For this reason, there is no decrease in EL luminous efficiency even in the blue light emitting element, and the maximum luminance is the same as the conventional Alq._ThreeIt is possible to make it larger than when using. In addition, since there is no passage of holes and power efficiency is good, power consumption can be reduced, and the device can be driven under low load conditions (low applied voltage), so that the lifetime of the element can be extended. Furthermore, by increasing the ionization potential of the electron transport layer, the energy gap of the blue light emitting layer can be increased, and therefore the emission wavelength can be shortened. As a result, it was possible to emit blue light with a color purity and chromaticity (0.25, 0.25) or less, which was difficult with conventional materials.
[0084]
In addition, since the electron transport material used in the present invention has a high glass transition temperature, excellent film formability and film quality stability, and high heat resistance, it is driven at a high temperature of 85 ° C., which has been poor at conventional organic EL devices, High heat resistance of the device, such as high temperature storage, was achieved.
[0085]
In addition, since an organic EL display can be manufactured using such an organic EL element, the display obtained can be increased in luminance and chromaticity, and the color 1/320 × 240 pixel simple matrix drive (Duty 1/120) can be achieved. A 4VGA panel can be produced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first configuration example of an organic EL element according to the present invention.
FIG. 2 is a diagram showing a second configuration example of an organic EL element according to the present invention.
FIG. 3 is a diagram illustrating a third configuration example of the organic EL element according to the invention.
FIG. 4 is a diagram schematically showing an energy diagram of materials used in the organic EL device according to the present invention.
FIG. 5 is a diagram schematically showing an energy diagram of materials used in a conventional organic EL element.
[Explanation of symbols]
1 Glass substrate
2 Anode
3 Cathode
4 Hole injection layer
5 Hole transport layer
6 Light emitting layer
7 Electron injection layer

Claims (8)

An organic EL element having a light emitting layer made of an organic compound thin film and an electron transport layer between different electrodes, and the light emitting layer emits blue light. The electron transport layer is represented by the following general formula (1). An organic EL device comprising a compound.
(M in the general formula (1) represents a trivalent metal atom having a higher ionization energy than aluminum. R ^{1 to} R ⁶ each independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or Represents an unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted cycloalkyl group or a cyano group, wherein at least one of R ^{1 to} R ⁶ is substituted Or an unsubstituted aryl group, and R ^{1 to} R ⁶ may be the same or different, and L is a halogen atom, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted group. A ligand having an alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted cycloalkyl group is represented. Represents 1 or 2, when n is 2, the groups represented by the same symbols R ¹ to R ⁶ may be the same or different.) The organic EL device according to claim 1, wherein R ^{4 in the} compound represented by the general formula (1) is an aryl group. The organic EL device according to claim 2, wherein the compound represented by the general formula (1) is a compound represented by the following formula (1a).
The organic EL device according to claim 2, wherein the compound represented by the general formula (1) is a compound represented by the following formula (1b).
  The organic EL device according to any one of claims 1 to 4, wherein the electron transport layer contains a plurality of compounds represented by the general formula (1). The organic EL device according to claim 5, wherein the electron transport layer contains a compound of the following formula (1a) and a compound of the following formula (1b).
The light emitting layer contains a compound represented by the following general formula (2) or the following general formula (3) and a compound represented by the following general formula (4). The organic EL element of any one of Claims.
(Wherein R _{1 to} R ₄ each independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an amino group, or a cyano group, and when n is plural, R _{1 to} R of different rings) ₄ may be the same or different, and R ₅ and R ₆ each independently represents an aryl group having 6 to 12 carbon atoms which may have a substituent, and n is Represents an integer of 3 to 6.)
(In the formula, M represents a metal atom, and R ^{11 to} R ¹⁹ each independently represent one selected from a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, and an aryloxy group, which may be the same or different. R ^{11 to} R ¹⁴ and R ^{15 to} R ¹⁹ may be bonded to each other to form a saturated or unsaturated ring, and R ^a has the same substituent as R ^{11 to} R ^19. R ^b is a hetero atom, R ^a and R ^b may be independently or bonded to each other to form a heterocycle, n represents 2 or 3, Represents a divalent group such as —O—.)
(In the formula, R _{21 to} R ₂₄ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an amino group, an alicyclic ring, or a heterocyclic ring; The groups having the same symbols represented by _{21 to} R ₂₄ may be the same or different, R ₂₅ and R ₂₆ each independently represents an aryl group which may have a substituent, and n is a positive integer. Represents.)   An organic EL display comprising the organic EL element according to any one of claims 1 to 7.